Regexp compile

Clean up mrbconf.h

fix access denied error at incremental build

- undef for windows is not used by default so comment it
- casting to the same type is not needed
- parenthesis are not needed for macro attributes separated by commas
- change order of MRB_NAN_BOXING and MRB_INT64 to simplify logic

declare local variable at the start of a block in generated gem_test.c

regexp parsing bug if unknown option is used

update String#gsub test

parser_dump supports NODE_REGEX.

MSVC: vars must be declared at the start of a block

Remove needless comment

Remove DISABLE_REGEXP

Changed debugger hook to disable

Added a hook at VM code fetch.

Pluggable regexp

add assert_{true,nil,equal} methods.